Transport aircraft typically include an environmental control system having one or more cooling systems for thermal management of the various systems of the aircraft. For example, an aircraft may include one or more air conditioning packs for controlling the temperature of the cabin and the cargo holds, and one or more galley chillers for temperature control of the galley carts which may contain perishable items. The aircraft may also include a power electronics cooling system (PECS) for cooling a high voltage direct current (HVDC) equipment rack of the aircraft. The HVDC may provide electrical power to various electronic components and devices on the aircraft. The PECS may circulate a cooling system fluid through the HVDC for maintaining the temperature of the HVDC within acceptable limits.
The aircraft may include a ram air circuit that may be fluidly coupled to the PECS for cooling the cooling system fluid. Air from outside the aircraft may be drawn into one or more adjustable ram air inlets mounted to the aircraft exterior surfaces. The ram air inlets may be configured to increase the pressure of the air drawn into the ram air inlets due to forward movement of the aircraft during flight. The air may be routed across one or more ram air heat exchangers for absorbing heat from the cooling system fluid. The heated air may then be discharged from the aircraft through one or more ram air outlets.
When the aircraft is moving at a relatively high speeds (e.g., 500-600 mph) at a cruising altitude where the ambient temperature is relatively cold (e.g., −50° F.), relatively large quantities of cold air may be drawn into the ram air circuit and may absorb a relatively large quantity of heat from the cooling system fluid. When the aircraft is parked on the ground and the ambient air temperature is relatively mild, a ram air fan may be activated to draw air into the ram air inlets and across the heat exchangers for maintaining the temperature of the cooling system fluid within acceptable limits.
However, when the ambient air temperature on the ground is relatively high, the ram air circuit may have a limited capacity for absorbing heat from the cooling system fluid. The reduced heat absorption capacity of the ram air circuit may affect the ability of the aircraft cooling systems to maintain the temperature of the HVDC, the air conditioning packs, and the galley chillers within operational limits. Although the temperature control capability of the aircraft cooling system may be improved by increasing the size of the ram air circuit, the confined space within the aircraft limits the extent to which the ram air circuit may be physically increased in size.
As can be seen, there exists a need in the art for a system and method for cooling the various aircraft systems when the aircraft is on the ground and the ambient air temperature is relatively high.